1. Field of the Invention
The present invention relates to electrical overcurrent protection devices, particularly electronic trip circuit breakers having a manually-controlled arc flash energy reduction system.
2. Description of Related Art
Overcurrent protection devices (OPDs) are used in electrical distribution systems to protect electrical conductors and equipment against the effects of short circuits, ground faults, and/or overloads (hereinafter “faults”). The OPDs in an electrical distribution system are often selectively coordinated so that the nearest OPD upstream to a fault will open and clear the fault before another further upstream OPD opens. Selective coordination of OPDs limits the number of distribution circuits that are de-energized by the operation of an OPD in response to a fault. However, selective coordination of OPDs may also result in added time delays that could allow more energy to be released during a fault than would have been released had the OPDs not been selectively coordinated.
The OPDs in an electrical distribution system can be circuit breakers having programmable electronic controllers for controlling the OPDs' trip settings. The programmable electronic trip controllers are known as electronic trip units and circuit breakers employing electronic trip units are known as electronic trip circuit breakers. Selective coordination among electronic trip circuit breakers is achieved by appropriately adjusting the trip settings of the electronic trip units.
Some electronic trip circuit breakers can be placed into a maintenance mode in which potential arc flash energy downstream of the circuit breaker is reduced. In maintenance mode, the circuit breaker uses trip settings (e.g., an instantaneous trip setting) that cause the circuit breaker to trip quickly, and tripping quickly reduces potential arc flash energy. The maintenance mode can be enabled through the use of a maintenance switch. A problem associated with the use of a maintenance switch is that an operator might fail to operate the maintenance switch prior to performing work downstream of the circuit breaker. For example, the operator might forget to operate the maintenance switch, or simply ignore the maintenance switch. It would be desirable to require that the maintenance mode be enabled before work is performed near energized equipment downstream of an electronic trip circuit breaker that is capable of being placed into the maintenance mode.